(a) Field of the Invention
The present invention is to install a transmission belt between two noncircular synchronous transmission pulleys, thereby providing a non-sliding synchronous transmission feature between the belt and the pulleys, when the noncircular active pulley is driven to synchronously link the noncircular passive pulley to rotate through the transmission belt, a noncircular synchronous transmission pulley set having periodically varying speed ratio and circumference compensating function is formed, through the two pulleys being formed with certain noncircular wheel shapes, during the synchronous transmission, the circumferences of the two wheel shapes can be mutually compensated, thereby when generating periodically varying speed ratios during the synchronous transmission, the tightness of the synchronous transmission belt can be remained the same or restrained within a smaller tightness varying level, a following pre-stressed idle wheel can therefore be optionally installed.
(b) Description of the Prior Art
Both or at least one of a conventional active pulley and a passive pulley are a circular pulley and the other is a noncircular pulley for forming performing the synchronous transmission, when the active pulley is driven in the revolving period, the active pulley performs the driving with periodically varying speed ratios to the passive pulley through a synchronous transmission belt, the tightness of the synchronous transmission belt installed between the circular pulley and the noncircular synchronous transmission pulley is often varied with respect to the varying speed ratios, even if a following pre-stressed idle wheel being installed, a situation of the transmission belt being released from the transmission pulley under high rotation speed may still occur.